Jet fuel compositions



United States latent 3,148,961 JET FUEL CQMPGMTiQNS Fred J. Dylrstra, Detroit, Mich, assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed Oct. 26, 1961, Ser. No. 147,721 5 Claims. (Cl. 44'76) This invention relates to new compositions of matter and in particular to new jet fuel compositions characterized by high thermal stability.

Fuel temperatures in modern jet aircraft power plants are becoming so high that harmful deposits are formed in the precombustion phase of the fuel system. Contributing to this has been the use of the fuel as a heat sink to aid in lubricating oil cooling, which has increased fuel temperatures to the point where deposits are so severe that they interfere with normal fuel combustion as well as lubricating oil temperature control. This is so serious a problem that it can eventually lead to engine failure of the turbine section due to uneven temperature patterns. In fact, it is considered the outstanding problem in jet fuels at the present time. Attempts have been made to counteract this by redesigning and by the use of shielding materials to minimize heating of the fuel. These methods are uneconomical and also contribute substantially to the overall weight of the aircraft.

It is an object of this invention to alleviate the thermal stability problems in jet fuels. It is another object of this invention to provide new compositions of matter. A further object is to provide new jet fuel compositions which are characterized by a high degree of thermal stability. Another object is to provide a process for cooling the lubricating oil in a jet engine.

The above and other objects of this invention are accomplished by providing a new composition of matter which comprises jet fuel containing from about 0.008 to about 5 percent by weight of an alkylene boronate in which the alkylene group contains from 2 to carbon atoms and is from 2 to 6 carbon atoms in length. Such compositions, as will be seen below, have a thermal stability of a magnitude which is well beyond that now possessed by any other commercial fuel.

In one embodiment of this invention, a jet fuel is treated with a fuel-soluble ester of an acid of boron in such a way that the fuel after treatment contains residual amounts of said ester. Thus, in this embodiment is provided a new composition of matter which comprises jet fuel containing a minor proportion of a fuel-soluble ester of an acid of boron. In this embodiment the ester of the boron acid is preferably one which is hydrolytically stable. This type of ester is preferred because it eliminates any loss of the boron compound when the fuel comes into contact with water during processing, shipment, storage and operation.

The hydrolytically stable esters of this invention are the glycol esters of boronic acids. In general, hydrolytioally stable esters of a boron acid can be considered to be any which are essentially unchanged after standing in contact with its volume of water at room temperature for at least 24 hours.

The present invention also has within its purview the process of improving jet fuel which comprises treating jet fuel with a fuel-soluble alkylene boronate.

The use of the fuel in modern jet aircraft as a heat sink as an aid in cooling lubricating oil has resulted in elevated fuel temperatures. It is. commonly known that conventional jet fuel normally tends to deteriorate when subjected to conditions of elevated temperatures below the cracking temperature of the fuel; i.e., temperatures in the range of from about 300 to about 500 F. Thus in another embodiment this invention provides a process for cooling the lubricadng oil in a jet engine comprising using as a coolant for heat transfer with said lubricating oil, a thermally stabilized jet fuel consisting essentially of distilled liquid hydrocarbon fuel having an end point of at least 480 F., said end point being higher than that of gasoline, said fuel containing from about 0.008 to about 5 percent by weight of an allcylene boronate containing up to about 26 carbon atoms in which the alkylene group contains from about 2 to 20 carbon atoms and is from 2 to 6 carbon atoms in length.

The alkylene boronate jet fuel additives of this invention have the formula wherein R contains from one to about 20 carbon atoms and is selected from the group consisting of alkyl, aryl, and cycloalkyl; and R is an alkylene group containing from 2 to 20 carbon atoms and is from 2 to 6 carbon atoms in length. In other words these alkylene boronates have a hydrocarbon group attached directly to the boron atom and an alkylene group bonded to boron through two oxygen atoms. It is preferable that the entire molecule contain from 3 to about 26 carbon atoms.

The boronates of this invention are cyclic esters of hydrocarbon boronic acids having the formula Preferred jet fuel additives of this invention are alkylene boronates containing a total of from 4 to 16 carbon atoms wherein the talkylene group is from 2 to 3 carbon atoms in length and is substituted with from one to 4 alkyl groups containing from one to 2 carbon atoms. The bydrocarbon portion bonded directly to boron is preferably an alkyl group containing up to about 12 carbon atoms,

a cycloalkyl group containing 5 to 6 carbon atoms, or an aryl group containing from 6 to 10 carbon atoms. Thus these preferred boronates are alkylene boronates having a fiveor six-membered ring composed of 2 or 3 carbon atoms, 2 oxygen atoms, and one boron atom. These boronates are preferred because they are miscible in all proportions in most jet fuels. Moreover, the five or sixmenrbered rings in these preferred boronates impart a high degree of stability to the additives.

Particularly preferred as a jet fuel additive are the (methylethylene) alkyl, aryl, and cycloalkyl boronates wherein the alkyl grou contains from about one to 12 carbon atoms, the aryl group contains from 6 to 10 carbon atoms, and the cycloalkyl group contains 5 or 6 carbon atoms. These compounds normally possess the excellent attributes of the preferred class or additives of this invention and are easily made from propylene glycol (1,2-dihydroxy propane) and the appropriate alkyl, aryl or cycloalkyl boronic acid. Using propylene gylcol is advantageous, for this is inexpensive and readily available. Thus, these particularly preferred alkylene boronates are very stable, very highly soluble in jet fuels, easily made, and economical. Furthermore, such compounds contain a high proportion of boron in the molecule.

The additives of this invention are more resistant to hydrolysis than most esters of boron acids known heretofore. This enhances the utility of the present alkylene boronates as additives to jet fuels because these esters, when dissolved in jet fuel, are not rapidly decomposed on contact with moisture which is normally present in most commercial jet fuels. The hydrolysis resistance of the present additives is attributable, at least in part, to the presence therein of the alkylene bridge.

Another outstanding feature of the additives of this invention is the fact that even when, under drastic conditions, they are hydrolyzed, the hydrolysis products thereof are themselves extremely resistant to hydrolysis and very soluble in jet fuel. Consequently, even though a jet fuel composition of this invention is agitated with large quantities of water, the boron dissolved in this fuel remains in solution in a suitable chemical form and continues to exert its beneficial functions. Furthermore, such drastic hydrolysis conditions do not result in the formation of insoluble sludges or other residue which would normally occur when using prior boron additives in jet fuels.

Still another feature of this invention is the fact that the present additives are easily made and inexpensive. Thus, this invention enables substantial improvements in the performance characteristics of jet fuels at low costs.

The jet fuels which comprise the major component of the new compositions of this invention are, in general, distilled liquid hydrocarbon fuels which are heavier than gasoline; i.e., they have a higher end point than gasoline. In general, the jet fuels can be comprised of distillate fuels and naphthas and blends of the above, including blends with lighter hydrocarbon fractions so long as the end point of the final jet fuel is at least 435 F., and preferably greater than 480 F. 4

These fuels include JP-3, a mixture of about 70 percent gasoline and 30 percent light distillate having a 90 percent evaporated point of 470 F.; J P-4, a mixture of about 65 percent gasoline and 35 percent light distillate, a fuel especially designed for high altitude performance; JP-S, an especially fractionated kerosene; low freezing point kerosene; etc.

The following are specifications of typical liquid hydrocarbon jet fuels of this invention:

Fuel A Fuel B Fuel Fuel D Fuel E Fuel F (JP-3) (J 1 -4) (.1 1 -5) (J P-4) (JP-4 (Kero- Referee) seue) Evaporated,

F 160 220 395 221 380 90% Evaporated,

F 470 470 480 379 460 480 End Point, F--- 600 550 550 480 516 Gravity, "APT 50 45 35 47. 3 48. 5 43 Existent Gum mg./

100 ml, max 7 7 7 1.0 1. 4 1. 7 Potential Gum,

nag/100 ml., max 14 14 14 1.0 9. 6 Reid Vapor Pres sure, p.s.i 7.0 3.0 Aromatics, vol.

percent 25. 0 25. 0 25. 0 12. 5 14. 6 14. 3 Olefins, vol. percent 5.0 5. 0 5.0 0.3 1. 2

The following examples illustrate various specific embodiments of this invention.

Example I To 100,000 parts of Fuel A is added with stirring 8 parts (0.008 percent) of 1,2-dimethyltrimethylene butaneboronate dissolved in 100 parts of xylene. The resulting fuel is found to possess improved thermal stability characteristics.

4 Example 2 To 100,000 parts of Fuel B is added 5000 parts (5 percent) 1,1,3-trimethyltrimethylene benzeneboronate. The resulting fuel possesses improved thermal stability prop erties.

Example 3 To 100,000 parts of Fuel C is added parts (0.1 percent) of 1,2-dimethylethylene benzeneboronate dissolved in 1000 parts of xylene. The resulting fuel blend possesses superior thermal stability characteristics.

Example 4 To 100,000 parts of Fuel D is added 500 parts (0.5 percent) of 1-propyl-2-ethylhexamethylene hexaneboronate. The resulting fuel blend is found to possess superior ther mal stability characteristics.

Example 5 To 100,000 parts of Fuel E is added 40 parts (0.04 percent) of 2-phenyl-4-methylpentamethylene dodecaneboronate dissolved in 600 parts of benzene. The resulting fuel blend possesses enhanced thermal stability properties.

Example 6 To 100,000 parts of Fuel F is added 200 parts (0.2 percent) of methylethylene l-methylpropaneboronate dissolved in 5000 parts of toluene. After mixing, the resulting fuel blend is found to possess enhanced thermal stability properties.

Example 7 Example 8 To 100,000 parts of a liquid hydrocarbon jet fuel having an end point of 550 F. is added 100 parts (0.1 percent) of 1,2-diethyltrimethylene cyclopentaneboronate. The resulting clear jet fuel containing this boronate possesses superior thermal stability properties.

Example 9 To 100,000 parts of Fuel A is added 15 parts (0.015 percent) of 1,6-diphenylhexamethylene benzeneboronate. This fuel, after mixing, possesses outstanding thermal stability characteristics.

Example 10 50 parts of 1,1,2,2-tetramethylethylene l-methylbutaneboronate is blended with 100,000 parts of Fuel B. The resulting jet fuel blend containing 0.05 percent of the boronate possesses outstanding thermal stability characteristics.

Example 11 To 100,000 parts of Fuel C is added 4000 parts (4 percent) of 1,2,3-triethyltrimethylene propaneboronate. The resulting jet fuel blend possesses superior thermal stability characteristics.

Example 12 To 100,000 parts of Fuel B is added with stirring 10 parts (0.01 percent) of methylethylene benzeneboronate. The resulting jet fuel is found to possess outstanding thermal stability characteristics.

Example 13 To 100,000 parts of Fuel D is added 100 parts (0.1 percent) l-benzyltrimethylene o-methylbenzeneboronate. After stirring, the resulting clear fuel possesses enhanced thermal stability characteristics.

Example 14 To 100,000 parts of Fuel F is added 600 parts (0.6 percent) of 1,4-dibutyltetramethylene octaneboronate. After stirring, the resulting fuel blend is found to possess outstanding thermal stability properties.

Example 15 To 100,000 parts of Fuel A is added 100 parts (0.1 percent) of l-methyl-Z-ethylethylene cyclohexaneboronate. The resulting fuel possesses improved thermal stability characteristics.

Example 16 To 100,000 parts of Fuel C is added 500 parts (05 percent) of methylethylene methaneboronate. The resulting fuel blend possesses outstanding thermal stability characteristics.

Example 1 7 To 100,000 parts of Fuel C is added 200 parts (0.2 percent) of l,1,2,2-tetramethylethylene benzeneboronate. The resulting fuel possesses outstanding thermal stability properties.

Example I 8 To 100,000 parts of Fuel B is added with mechanical stirring 0.04 percent of 1,1,3-trimethyltrirnethylene octaneboronate. The finished fuel containing this additive is found to possess superior thermal stability properties.

The substantial improvements which result from addition of these agents to jet fuel is illustrated by tests in an apparatus known as the Erdco Fuel Coker. This unit and the method of using it are described in Petroleum Processing, December 1955, pages 1909-11. The apparatus consists of a heated sintered steel filter through which a preheated fuel is passed at a regulated rate. The time which it takes for the pressure drop across the filter to reach 25 inches of mercury is taken as a measurement of the coking tendencies of the fuel and, therefore, as a measurement of the fuels thermal stability characteristics. A fuel that runs through the apparatus for a full 300 minutes without causing any pressure drop is considered thermally stable. The ideal fuel would pass through the filter indefinitely without causing any pressure drop.

To demonstrate the substantial improvements in high temperature stability exhibited in jet fuels of this invention, recourse is had to the above Erdco Coking test. Samples of jet fuels of this invention, such as those appearing in the above examples, are subjected to the Erdco Coking test. The conditions used in this test are as follows: Unit operated at 150 p.s.i. with the pre-heater temperature at 325 F., the filter temperature at 500 F., and a residence time of 30 seconds. For comparative purposes, the corresponding boronate-free base fuels are likewise subjected to this test. It is found that in all instances the presence in the fuels of the boronate causes a substan tial increase in the time required for a pressure drop of 25 inches of mercury across the filter to occur. Furthermore, the majority of the fuels of this invention formulated from base fuels requiring at least 150 minutes for this pressure drop to occur do not reach this pressure drop even in the full 300 minutes. In some cases the pressure drop achueved with these last-named jet fuels of this invention is less than inches of mercury after 300 minutes.

As an example of the outstanding potency of alkylene boronates in improving the high temperature stability characteristics of jet fuels, comparative Erdco Coking tests are conducted under the conditions specified above.

The base fuel used is a JP-4 referee fuel having the following inspection data.

Gravity, API 48.5 Vapor pressure 2.8 Distillation, initial, F

5 10 15 268 20 28-7 50 354 460 .Final 516 Mercaptan sulfur, percent 0.001 Freezing point, F 67 Aromatic, vol. percent 14.6 Olefins, vol. percent 1.2 Existent gum, mg./ m1. 1.4 Potential gum, rug/100 ml. 9.6

Total sulfur, percent 0.193

When this additive-free base fuel is tested for its thermal stability in a pair of tests, it was found that a pressure drop of 25 inches of mercury occurred after 27 and 32 minutes. Two individual portions of this same base fuel, each containing 0.17 percent by weight of alkylene boronate such as methylethylene butylboronate show a substantial increase in the time of this pressure drop. Thus, typical fuels of this invention possess a thermal stability substantially greater than the corresponding boronate-free base fuel.

Similar results are obtained with other jet fuel compositions of this invention; i.e., hydrocarbon jet fuels containing from about 0.008 to about 5 percent by weight of any boronate described by the general formula appearing above.

The jet fuel compositions of this invention possess outstanding high-temperature stability characteristics by the presence therein of such additives as tetramethylene butaneboronate; 1 methyl 3 isopropylhexamethylene :benzeneboronate; 2 ethyl 4 phenylpentamethylene hexaneboronate; 2 tert butyl 4 propylpentamethylene octaneboronate; 2 propyl 4 tolyltetramethylene dodecaneboronate; 2 cyclohexyl 3 propylpentamethylene trimethylmethaneboronate; 1 phenyl 2 methyl 3- ethyltetramethylene cyclopentaneboronate; 1,2,3,4 tetramethylhexylene 2 phenylethaneboronate; 1,5 dipropylpentamethylene 4 tert butylbenzeneboronate.

Among the preferred additives of this invention are 1,3- diethyltrimethylene n-octaneboronate; 1,1-dimethyl-2,2- diethylethylene 1 methylpropaneboronate; 1 ethyl 3- rnethyltrimethylene benzeneboronate; 1,2 dimethylethylene cyclohexaneboronate; 1,2,3 triethyltrimethylene cyclopentaneboronate; methylethylene butaneboronate; methylethylene 1 methylethaneboronate; 1,3 diethyltrimethylene 4 ethylbenzeneboronate; 1,2 dimethylethylene 1 phenylethaneboronate; methylethylene methaneboronate.

The additives of this invention are prepared by heating a hydrocarbon boronic acid with an appropriate acyclic diol meeting the requisites set forth above in the presence of an azeotroping solvent to remove the water for-med during the reaction. One molecular equivalent of hydrocarbon boronic acid is reacted with approximately one molecular equivalent of the diol, and 2 molecular equivalents of water are removed as an azeotrope with the solvent. Suitable azeotroping solvents include benzene, toluene, xylene, natural hydrocarbon fractions boiling in the range of about 75 to C. or the like. The mixture of boronic acid, diol, and an azeotroping solvent is heated to the reflux temperature-usually from about 75 to 150 C. On completion of the reaction, as evidenced by cessation of water evolution, the resulting product comprises the alkylene boronate dissolved in the azeotroping solvent. If desired, the boronate can then be removed from the solution by distilling oif the solvent: The boronate remaining in the distillation vessel can then be, purified by vacuum distillation if desired. Alternatively, the solution of the boronate in the azeotroping solvent in which it was formed may be used as the for-mue lation in subsequent blending operations with jet fuels. A further advantage of using the solution is that it enhancesthe stability of the boronate. Thus, by using such solutions, the presence of the" desired quantity of the alkylene boronate in the resulting jet fuel blend is assured; none of the boronate has been decomposed even when this solution is stored for long periods of time.

The amount of alkylene boronate used in the jet fuels of this invention can range from about 0.008 to about percent by weight. Ordinarily, amounts of from 0.1 to 0.2 percent are found to be quite effective. Variations from these concentrations are permissible. For example, in jet fuels initially possessing a fair degree of thermal stability, very small amounts of the above boronates are suflicient to greatly improve the thermal stability characteristis of such fuels. On the other hand where the jet fuel initially has a very poor thermal stability, larger amounts (about 4 to 5 percent by weight or more) can be effectively used.

' This application is a continuation-in-part of my copending application Serial No. 576,776, filed April 9, 1956, now U.S. Patent 3,009,797.

I claim:

21. As a new composition of matter, jet fuel consisting essentially of distilled liquid hydrocarbon fuel having a higher end point than gasoline, said end point being at least 480 F., containing from about 0.008 to 5 percent by weight of an alkylene boronate having the formula least 480 F., containing from about 0.008 to 5 percent by weight of an alkylene boronate having the formula wherein R is a hydrocarbon group selected from the class consisting of alkyl radicals containing 1 to 12 carbon atoms, aryl radicals containing 6 to 10 carbon atoms and cycloalkyl radicals containing 5 to 6 carbon atoms, and

R is an alkylene group of 2 to 3 carbon atoms in length and is substituted With 1 to 4 alkyl groups containing 1 to 2 carbon atoms, said boronate molecule containing a total of 4 to 16 carbon atoms.

3. The process for cooling the lubricating oil in a jet engine comprising using as a coolant for heat transfer of said lubricating oil, a thermally stabilized jet fuel consisting essentially of distilled liquid hydrocarbon fuel having a higher end point than gasoline, said end point being at least 480 F., said fuel containing from about 0.008 to 5 percent by weight of an alkylene boronate having the formula wherein R is a hydrocarbon group containing from 1 to 20 carbon atoms and is selected from the group consisting of alkyl, cycloalkyl and aryl, and R is an alkylene group containing from 2 to 20 carbon atoms and being from 2 to 6 carbon atoms in length, said boronate molecule containing 21 total of 3 to 26 carbon atoms.

4. The process for cooling the lubricating oil in a jet engine comprising using as a coolant for heat transfer of saidlubricating oil, a thermally stabilized jet fuel consisting essentially of distilled liquid hydrocarbon fuel having a higher end point than gasoline, said end point being at least 480 F., said fuel containing from about 0.008 to 5 percent by weight of an alkylene boronate having the formula 0 RB V\R wherein R is a hydrocarbon group selected from the class consisting of alkyl radicals containing 1 to 12 carbon atoms, aryl radicals containing 6 to 10 carbon atoms and cycloalkyl radicals containing 5 to 6 carbon atoms, and R is an alkylene group of 2 to 3 carbon atoms in length and is substituted with 1 to 4 alkyl groups containing 1 to 2 carbon atoms, said boronate molecule containing a total of 4 to 16 carbon atoms. 5. The composition of claim 1 wherein said alkylene boronate has the formula I/ OO\ CsHn- /C z 

1. AS A NEW COMPOSITION OF MATTER, JET FUEL CONSISTING ESSENTIALLY OF DISTILLED LIQUID HYDROCARBON FUEL HAVING A HIGHER END POINT THAN GASOLINE, SAID END POINT BEING A LEAST 480*F., CONTAINING FROM ABOUT 0.008 TO 5 PERCENT BY WEIGHT OF AN ALKYLENE BORONATE HAVING THE FORMULA 